Keaton Kristick is having a blast, man

Keaton Kristick is a backup inside linebacker on a team that includes Patrick Willis and Takeo Spikes, which means the undrafted rookie free agent is receiving quite an education this season.

Last week, for example, Kristick got an eye-opening glimpse into NFL-style toughness.

Willis and Spikes both played in a 34-7 loss at San Diego with broken right hands covered by large black casts.

Spikes finished with 12 tackles. Willis, who played three days after surgery to insert a pin in his hand, had eight tackles.

Was Kristick in awe of his teammates?

The 22-year-old flashed a wide no-duh smile when asked the question Friday.

“You could say that, man,” said Kristick, who sports a scraggly mop of black hair. “I didn’t even know what to expect going into the game. There were times in college where I was like ‘My finger hurts.’”

Kristick is about as likeable as Spikes and Willis are tough.

Most of the 49ers are polite when fielding questions from the media.

Kristick, happy to discuss wrestling moves once the tape recorder is turned off, might be the only one who could accurately be described as eager.

Kristick’s father (Northern Illinois), older brother (New Mexico) and uncle (Army) all played college football. And the longshot to survive training camp is clearly thrilled to be able to keep playing after earning first-team all-Pac 10 honors as a senior at Oregon State.

Kristick spent the season’s first four weeks on the practice squad — he was promoted when safety Michael Lewis was released — and has since been inactive in five of 10 games.

He has played on special teams, but got his first extensive playing time on defense in the fourth quarter of the Niners’ 40-21 blowout of the Seahawks. He flashed his speed, energy and instincts while collecting six tackles, according to NFL stats. He had two tackles in limited action against San Diego.

“It was a blast, man,” Kristick said of his NFL baptism against Seattle. “It was a blast. Just running around. I told some guys on the field, ‘I don’t even care if I mess up on a play.’ It was just the sheer excitement of actually getting out there and just playing ball and letting your instincts do everything. I was having a blast. Every time I step on the field I have fun.”

The 6-foot-3 Kristick will likely need to add bulk and brawn to earn an expanded role in the future. He chugged chocolate milk at Oregon State to keep his weight up during the season and he still looks a few gallons shy of his listed weight of 234 pounds.

As for his attitude, his enthusiasm might not be too unusual for an undrafted rookie free agent on the fringes of an NFL roster.

Even if he learns to channel Willis and Spikes, though, it’s hard to imagine him not having a blast for as long as he’s playing professional football.

“It’s so great being able to go out on the football field and play the game you enjoy,” Kristick said. “I’m just grateful to this organization for giving me the opportunity. I’m so thankful for that. So thankful.”